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CU-Boulder IPHY 4440 - Corticoid Synthesis
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IPHY 4440 1st Edition Lecture 6Outline of Last Lecture I. NomenclatureOutline of Current Lecture II. Corticoid synthesisIII. Vitamin D synthesis IV. Steroid transport V. Metabolism of steroidsCurrent LectureI. Corticoid synthesis Pathway: Progesterone (precursor to all corticoids)  x P450 C11 (add hydroxyl group)  Cortisol or Corticosterone (both C21)  p450 aldo aldosterone (ketone group on C18)Note: enzyme P450 C11 only located in the mitochondria A. Cortisol: in humans, precursor for aldosterone, released when stressedB. Corticosterone: in animals, - Only difference is the side chain between those two II. Enzyme - action review1) P450 scc (located in mitochondria) ~ action: Cholesterol to pregnenolone 2) P450 c11 ~ action: progesterone  cortisol or corticosterone3) 3B-HSD ~ action: Pregnenolone  progesterone4) 5 a-reductase ~ action: Testosterone  DHT5) P450 aro ~ action: testosterone  estrogen6) P450aldo ~ action: Corticosterone  aldosterone III. Vitamin D synthesisThree organs involved: skin, liver, kidneyRole in calcium homeostasis Need Vitamin D to properly regulate bone density, absorbs calcium from diet Pathway: cholesterol  Sun, UV light (rate-limiting step) zaps the ring of steroid nucleus open Cholecalciferol (Vitamin D3) not biologically active yet  liver  kidney where it is biologically active These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Key: Vitamin D started as a steroid but since the steroid nucleus gets destroyed, Vitamin D is not a steroid in its final formIV. Steroid Transport Steroids are extremely hydrophobic so they need steroid binding proteinsA. Sex steroid binding globulin (SBG) = androgen binding protein i. Binds T, DHT, E2 ii. Binds DHEA and androstendione but weakly b. Corticosteroid binding globulin (CBG) = transcortin (transport corticosteroids)i. Binds cortisol, corticosterone ii. Some progesterone NOT aldosteroneiii. Aldosterone travels in its “naked” form in the blood or weakly binded to proteins in blood whereas steroids never travel “naked” in the bloodVI. Metabolism of steroidsA. Conjugation: make water soluble, add highly charged/polar molecules to make it water soluble by adding a sulfate or glucuronic acidB. When conjugated can no longer bind to binding proteins or receptors and becomes biologically inactive C. Converted to inactive formi. Corticoids  corotic acids ii. Estrogens catecholsiii. Catechols: contains an aromatic ring with 2 hydroxyl groups next to each other ex: dopamine, NE, Eiv. Catechol estrogen: cannot bind to an estrogen receptor or act like an estrogen VII. NeurosteroidsA. Brain DHEA and pregnenolone > plasma level B. Brain levels persist after gonadectomy (remove gonads) C. Enzymes observed in the brain: P450scc, 3B-HSD, 5a-reductase, P450aro- Brain has all key enzymes for steroid synthesis - Production of steroids can occur in many places in the body but the brain is one of the primary places that have all 4 of the key enzymesVIII. Thyroid HormonesA. Synthesis: From tyrosine (part of thyroglobulin) B. Hormone contains iodine- Produced as biologically inactive form- Only hormone that contains halogensC. Ionic form: iodide (I-) need enough iodide for thyroid synthesis D. Tyrosine is strung together in a protein chain in order to make TgB (Thyroglobulin)IX. Iodination of TyrosinesA. Joined to amino acid, part of TgBB. Tyrosine has an aromatic ring (6 carbons)C. MIT= 3-monoiodotyrosine  Iodine positioned first and stuck to carbon 3 D. MIT= first step of thyroid synthesis E. DIT: 3,5-diiodotyrosine F. Coupling of 2 DITS: aka a form of thyronine  2 a-rings joined together by O and creates the first form of thyroid hormones G. Thyroxine (T4): biologically active so called a hormone can be converted with one step to a biologically active state H. Thyroid peroxidase (TPO): iodination and coupling controlled-Released as free T4 into blood I. Deiodination of T4: Take off the outer ring iodide (take off I’5) to convert to T3 (biologically active) - Occurs in liver & target cells J. Reverse T3: rT3 (inactive), occur in very low levels in the blood, rT3 cannot bind to binding proteins so get metabolized easily, remove I on carbon 5, occurs primarily in liver to get metabolized so way of body getting rid of T4 or


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CU-Boulder IPHY 4440 - Corticoid Synthesis

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